Extremely large earth digging buckets, such as used in dragline and large shovels, have increased in size to the point where many such buckets dig upwardly of 100 cubic yards of earth in a single bite. Such buckets have an open front with a digging lip at the bottom equipped with forwardly projecting teeth to aid in penetrating the earth in loading the bucket. The teeth on the bucket digging lip are cast metal of a type which is resistant to abrasion, yet, in use, the severe circumstances of operation do wear the teeth, requiring replacement from time to time to maintain the bucket's efficiency in digging. In many typical installations, a tooth base is welded to the bucket lip and extends forwardly therefrom, and has a nose part at the front upon which a tooth holder is removably mounted. This holder, in turn, has a nose part at its front upon which a replaceable toothpoint is held with a fastener in such a fashion that it can be replaced. The assemblage of the tooth base holder and toothpoint extend forwardly from the bucket lip a considerable distance. In a 60 cubic yard size bucket, this assembly may extend typically about 26" forwardly of the cutting lip of the bucket, and for a 120 cubic yard size the extension of the assemblage may be as much as 30" in front of the bucket lip. These teeth are subject to quite large stresses even though the parts are quite large and quite heavy. In the larger size, a typical 10" wide toothpoint would weigh as much as 150 pounds, its mounting holder about 390 pounds, and the tooth base welded to the bucket lip as much as 850 pounds. The size and the weight of the teeth is such that it is desired not to increase the same to provide resistance to breakage. The abrasion on the toothpoint is such that experience has taught that toothpoints are replaced in about a 4:1 ratio to the tooth holder. Even though the parts are quite large and heavy, experience has also indicated that breakage of the assembly most often occurs at the base of the toothpoint where the tooth holder nose will be fractured in its largest section at the base of the nose. It would be desirable to provide internally of the assembly of the toothpoint to its holder, a structure which would be more resistant to this breakage.
In the past, various attempts have been made to design the internal fitting parts of a tooth and its base to adequately resist the forces to which it is applied in use. Typical of such attempts are interfitting tangs and grooves, such as shown in U.S. Pat. No. 2,483,032; the provision of a spherical interfitting surface between the parts to reduce bending stresses, such as shown in U.S. Pat. No. 2,919,506; an arrangement of contact areas between a tooth and its support in an attempt to prevent force reaction and stress concentration points, such as shown in U.S. Pat. No. 3,508,352; and the provision of multiple fastening devices between a tooth and its base to reduce stresses, such as shown in U.S. Pat. No. 3,774,324.